1. Field of the invention
The present invention relates to a measurement apparatus and a measurement method for measuring a specific biological component in a biological sample collected by puncturing a living body. Specifically, the present invention relates to a biological component measurement method and apparatus for storing, processing, and/or displayed measurement values in association with a sample collection site.
2. Description of the Related Art
Up to now, various types of biosensors utilizing specific catalytic actions of enzymes have been developed. Specifically, glucose sensors for quantifying glucose are widely used for measurements of blood glucose levels (glucose concentrations in blood) in clinical examinations. Hereinafter, the glucose sensors will be discussed as an example of the biosensors.
As a method for electrochemically quantifying glucose, a method that utilizes glucose oxidase (EC1.1.3.4; hereinafter abbreviated as GOD), which is an enzyme, and an oxygen electrode or a hydrogen peroxide electrode is generally known (e.g., “BIOSENSOR” edited by Shuichi Suzuki, KODANSHA, March 1984, pp. 100-101).
Although this method accurately quantifies glucose in a biological sample by making use of the specificity of an enzyme reaction, it has a disadvantage that measurement results are affected by oxygen concentration within the sample. If there is no oxygen in the sample, no measurements can be performed.
Accordingly, there have been developed glucose sensors of a new type that does not utilize, as an electron carrier, oxygen but utilizes organic compounds such as potassium ferricyanide, ferrocene derivatives, quinone derivatives and so on, or metal complexes.
By utilizing the organic compound or the metal complex as an electron carrier, glucose can be accurately quantified without being affected by the oxygen concentration in a biological sample.
In addition, in this case, a reagent layer containing an enzyme and an electron carrier can be integrated with an electrode system under almost dry conditions, and therefore, it is possible to produce disposable glucose sensors based on this technology, and such glucose sensors have recently come into widespread use.
As for a disposable glucose sensor, glucose can be readily measured with a measurement apparatus by merely introducing a biological sample into the sensor that is detachably connected to the measurement apparatus (see, for example, Japanese Laid-open Patent Publication No. 03-202764).
The widespread use of the glucose sensors such as the above has made it possible for patients with diabetes to readily measure their blood glucose levels at home. As the procedure, a method as described below is common.
Initially, a collection site is punctured by means of a needle attached to a puncture apparatus. Then, a biological sample (i.e., blood) is squeezed out from the punctured site. Finally, a sensor, which has been previously attached to a measurement apparatus, is brought close to the punctured site so as to cause a biological sample supply opening of the sensor to be in contact with the squeezed blood, thereby supplying the blood into a sample chamber of the sensor. The biosensor detects glucose in the blood thereby quantifying the amount of glucose contained in the blood. Regarding measurements using a glucose sensor as described above, a substrate concentration in a biological sample can be readily measured using a biological sample in an amount of the order of a few μl.
When measuring blood glucose levels, conventionally, it is common to collect blood by puncturing a fingertip. However, in recent years, a method, which collects blood from, for example, a forearm rather than a fingertip, to measure blood glucose levels has come into use.
This method is advantageous in, for example, that no scar remains in fingertips after puncturing, and the puncture is less painful because forearms are not as sensitive as fingertips. Thus, diabetes patients are provided with more options for measuring their own blood glucose levels.
Recently, with intent to further simplify the measurement procedure, products that combine a puncture apparatus and a measurement apparatus for glucose sensors have become commercially available. These products have an advantage that puncturing by the puncture apparatus and measurement by the sensor can be performed with a single measurement apparatus, whereby it is possible to reduce the number of measurement steps that a patient with diabetes has to go through.
An example of such a conventional combined measurement apparatus is a biosensor measurement apparatus (Sof-Tact™) for measuring glucose at levels from a forearms, which is currently commercially available from Abbott Laboratories. FIG. 11 shows a schematic diagram thereof.
As shown, a measurement apparatus 91, which has attached thereto a biosensor for measuring glucose in blood and a puncturing member for puncturing a living body, includes a switch 93 for starting a measurement, a display member 92 for displaying obtained results, and a contact surface 96 for contact with a living body. Contact surface 96 includes a collection opening 97 through which the puncturing member protrudes to collect blood extracted from a living body. The biosensor apparatus of this configuration is designed such that the contact surface for contact with the living body fits a forearm, and therefore, it is difficult to collect samples from another location (e.g., a fingertip).
On the other hand, it has been reported that when the concentration of glucose in the blood varies largely, for example, immediately after a meal, measurement values of glucose concentrations obtained by biosensors vary among different blood collection sites (for example, a fingertip, a forearm, a thigh, etc.) even in the same subject (e.g., John M. ELLISON, Diabetes Care Vol. 25, No. 6, 961-964, (2002)). Therefore, even with the same subject, depending on the elapsed time after the meal, there may occur a problem where an actual measurement value of a sample collected from a forearm, for example, cannot be compared directly with standard values based on samples collected from a fingertip.